Damn that was hard to decide, i thought the skarrj hybrids were the coolest(loved being the skarrj called Disconnect) but im afraid it just loses out to ut2004 tusked models by a tiny, TINY, bit. as for the rest it would go like this:
3rd place
Mecha Skarrj - Ut2004 ECE
4th Place
Uc2 Skarrj
5th Place
Unreal 2(the ones i saw were horribly wide, and lacked any air of malice or intimidation)
cannot say: unreal 1 because i never played it, i hope to in the future though, but i heard that copies are hard to come by